1. Field of the Invention
The field of art to which this invention pertains includes shift control systems for multiple input-multiple output transmissions which provide a plurality of speed ratios in response to the movement of an operator's shift lever or the like.
2. Description of the Prior Art
U.S. Pat. No. 4,000,662 assigned to the assignee of the present invention discloses a similar gear train as disclosed herein. U.S. Pat. No. 4,068,537 also assigned to the assignee of the present invention discloses a sophisticated shift control system of the preselector or semi-automatic type wherein shifts between drive ratios are made in response to the movement of an operator's shift lever and the release of the torque on the drive train.
A manual shift control system is jointly disclosed in U.S. Pat. Nos. 4,155,271, 4,170,148 and 4,197,760, all assigned to the assignee of the present invention, utilizing input and output control shafts. The control shafts are rotatable in response to shift lever movement. An interlock system is disclosed which prevents simultaneous rotation of input and output control shafts to thus prevent the overlapping of input and output shift rail movement. Each cam shaft included one-way and two-way cams of the initial shift without overtravel type selectively capable of cooperation with input and output shift rails. The resultant increased throw of the shift lever to accomplish a change in speed ratios in the above-discussed manual control system requires a relatively large operating area for the shift lever.
Also disclosed in prior art transmission control systems are screw driven control shafts having cams mounted thereon as shown in United Kingdom Pat. No. 1,306,117 and U.S. Pat. No. 3,429,194. Although the abovediscussed screw driven control shaft type of transmission is somewhat more simplified in design, one disadvantage is that the operator is unable to bypass a speed ratio during speed changes.
Other prior art transmissions of interest to the present invention are U.S. Pat. Nos. 1,118,389, 1,229,301, 1,928,782, 2,812,667, 2,853,889, 3,431,791, 3,487,713 and 3,857,299.